The present invention relates to a damped bearing device suitable for use in high-speed rotary machines and, more particularly, to a damped bearing device for use in high-speed rotary machines which undergo several critical speeds in the course of acceleration to the high running speeds.
It is a current tendency that rotary machines undergo several critical speeds when the machines are accelerated to the normal high running speed after the starting. When the rotary machine undergoes a critical speed, the amplitude of vibration thereof is increased to increase the force transmitted to the bearings to shorten the life of the bearing or to damage the same. In the worst case, the rotor of the machine itself becomes inoperative.
From view points of realization of high speed operation, as well as assurance of long life of the bearing, it is an important and effective measure to provide the bearing with a vibration damping means. An example of such a vibration damping means is disclosed in the specification of U.S. Pat. No. 3,456,992. This vibration damping means is constituted by a spring portion for resiliently supporting the bearing and a damper portion consisting of a squeeze film provided on the periphery of the bearing. If this known vibration damping means is used for a large-size machine of a heavy weight, the bearings are largely deflected downward by the weight of the rotor, because the latter is supported resiliently. In consequence, the vertical gap for the squeeze film in the damper portion becomes non uniform thereby deteriorating the damping effect of the damper portion. This in turn gives a rise to a demand for a structure for compensating for the deflection due to the weight of the rotor. Examples of such structures are shown, for example, in the specification of the U.S. Pat. No. 4,027,931 corresponding to German Pat. No. 2644026 and to Swiss Pat. No. 612,250.
In the damped bearing devices of the kind described, it is essential for sufficiently reducing the amplitude of vibration that the spring rigidity of the spring portion and the damping effect of the damper portion are istopropic with respect to the rotor, i.e., uniform in every radial direction of the rotor. In the conventional damped bearing devices, however, no specific consideration have been made for obtaining an isotropic of the spring rigidity and the damping effect. In addition, since the space in which the squeeze film of the damper portion acts is comparatively small, it requires an extremely delicate and minute work to maintain this space at the design value, taking into consideration the machining and assembling works.